Synthesis and characterization of nanocrystalline barium strontium titanate powders prepared by citrate precursor method

Nanocrystalline and well dispersed barium strontium titanate (BST) powders were prepared by a novel and simple citrate precursor method. This method involved direct crystallization of a white precursor from a stable solution in the citric acid (CA)–ethylene glycol (EG)–tetrabutyl titanate–M²⁺ (M = Ba, Sr) system under a specific pH value range. Subsequent heat treatment of the precursor at 850 °C led to a pure phase BST powder. TG/DTA was used to examine the decomposition behaviour of the precursor. The crystalline phase and morphology of the BST powders were investigated by XRD and TEM. It was found that the BST powders synthesized by citrate precursor process were more homogeneous and uniform than that obtained by the citrate gel method.     

Synthesis and properties of manganese-doped barium titanate

An oxalate route for the production of BaTiO₃ has been modified to incorporate Mn (upto 2%) as a dopant and the reaction sequence has been studied. The resulting Mn-doped BaTiO₃ exhibits a dielectric constant with an increasing insensitivity to temperature and applied a.c. field as the Mn content is increased. These samples possess a high electrical resistivity even after treatment in hydrogen at 1100°C and are therefore suitable as dielectric for multilayer capacitors with base metal electrodes.     

Synthesis of barium titanate nanopowder by a soft chemical process

A simple soft chemical method of synthesizing barium titanate nanopowders and nanorods is described here, where titanium dioxide/titanium isopropoxide was taken as a source of titanium, tartaric acid was taken as a template material, nitric acid as an oxidizing agent. The synthesized powders and rods were characterized by XRD, TG and DTA, SEM and IR spectroscopy. In this process phase pure barium titanate nanopowders and nanorods can be prepared at a temperature of 900 °C and the process is simple and cost-effective.     

Synthesis of single-crystal barium titanate nanorods transformed from potassium titanate nanostructures

Single-crystal barium titanate (BaTiO₃) nanorods were synthesized by a hydrothermal reaction using precursors of potassium titanate (K₂O·nTiO₂, n = 4 or 6) nanostructures. The precursors of potassium tetratitanate (K₂Ti₄O₉) and potassium hexatitanate (K₂Ti₆O₁₃) nanostructures were prepared by a sol-gel method in which a growth of K₂O·nTiO₂ (n = 4 or 6) nanorods was induced by a role of pre-crystallized K₂O phase at defined heating temperatures. The specific morphologies of BaTiO₃ nanorods featured with flat or stepped surfaces and rectangular or polygonal cross-section, were obtainable by selecting the structure of precursors.     

Synthesis of barium strontium titanate nanorods in reverse microemulsion

Perovskite Ba_0.7Sr_0.3TiO₃ nanorods were synthesized in Triton X-100 reverse microemulsion at room temperature and characterized by XRD, ICP-AES, ED and TEM. The Ba_0.7Sr_0.3TiO₃ nanorods with a diameter of 60-100 nm and a length of 450-1200 nm showed a single-crystalline tetragonal structure. The size of nanorods was effectively tuned by changing w value (molar ratio of water to surfactant), aging time and reactant concentration.     

Synthesis, microstructure and dielectric properties of zirconium doped barium strontium titanate obtained by solvothermal method

(Ba_0.8Sr_0.2Zr_yTi_1?yO₃) (y = 0.05, 0.1, 0.15 and 0.2) nanosized powders is synthesized by solvothermal method. The formation of (Ba_0.8Sr_0.2Zr_yTi_1?yO₃) was confirmed by XRD, FT-IR and XPS analysis. The purity of the (Ba_0.8Sr_0.2Zr_yTi_1?yO₃) was examined using FT-IR spectroscopy. The X-ray analysis proves that all as-synthesized Ba_0.8Sr_0.2Zr_yTi_1?yO₃ powders have a cubic perovskite structure. The surface characterization indicates the powder contains Zr and Sr elements. SEM investigation shows that the average particle size is reduced with increasing the Zr content and the average particle size is in the range 37–50 nm, the well dispersed nano powders have narrow particle size distribution. The study of dielectric properties shows that the Curie peaks of dielectric constant become broader and shift towards lower temperature on the basis of Ba_0.8Sr_0.2TiO₃ and the dielectric loss decreases with increasing Zr content.     

以偏钛酸为原料常压水热法合成纳米钛酸钡的研究

系统地研究了以廉价的偏钛酸为原料,经常压水热法一步合成钛酸钡.通过考察不同的钡钛比,反应温度,反应时间,溶液pH等条件下反应产物在浓盐酸溶液中的透射比的变化,得出了最佳的制备条件.当反应原料的钡钛比为1.4,反应温度是100℃,反应时间为6 h,溶液pH为12,所制备出的钛酸钡粉体为立方相,a值约为4.030,粉体一次平均粒径为40.9 nm.     

微乳液-共沸蒸馏法制备钛酸钡纳米粉体

以水/正辛烷/正己醇/司班80油包水体系中的微乳液滴为纳米反应器,通过微乳液滴中增溶的醋酸钡和油相中草酸酰化的钛酸四丁脂反应生成钛酸钡前驱体,并通过共沸蒸馏去除前驱体中的水分,以减小煅烧过程纳米钛酸钡粉体的团聚.实验结果表明,此方法制备的前驱体只需在550℃煅烧就可以生成钛酸钡晶粒,只需在600℃煅烧10min就可以得到粒径只有40nm左右的高纯立方钛酸钡纳米粉体,而且粉体具有粒度分布窄、形貌规则、优越的钛钡摩尔比、低团聚等优点.     

Semiconducting properties of barium titanate and iron substituted barium titanate

Single crystals of barium titanate and members of the series BaTi_1?xFe_xO_3?xF_x have been grown from a potassium fluoride flux. These crystals were made conductive by heating in a sealed evacuated silica tube in the presence of freshly ground titanium. Electrical, optical and magnetic measurements were performed in order to characterize these crystals. Optical measurements indicated a decrease in the band edge from 3.2(1) eV for barium titanate to 2.8(1) eV for Bati_1?xFe_xO_3?xF_x(x = 0.02, 0.05, 0.07, 0.10). The photoelectrolytic behavior of reduced barium titanate was strongly quenched upon the substitution of iron and fluorine.     

Synthesis of nm-sized barium titanate crystallites using a new LTDS method and their characterization

A new LTDS method was established to synthesize nm-sized barium titanate crystallites with particle sizes around 10 nm. This LTDS method was the following two features, i.e., (1) a heat of neutralization in a neutralization reaction between strong acid and base can be used as a driving force for a formation of barium titanate, and (2) barium titanate crystallites can be directly synthesized from Ti and Ba ions, not via intermediates. Therefore, using the LTDS method, it can be expected that there is no minimum limit in particle sizes, and also no contamination in barium titanate crystallites. At first, optimum conditions for a formation of barium titanate were screened at various reaction temperatures and Ba/Ti atomic ratios in the starting materials. As a result, the formation of barium titanate was found at higher reaction temperatures than 50°C and higher Ba/Ti atomic ratios than 5. Under a constant temperature, particle sizes decreased with increasing Ba/Ti atomic ratios while under a constant Ba/Ti atomic ratio, particle sizes were independent of reaction temperatures. Finally, barium titanate crystallites with particle sizes below 10 nm were first prepared. These particles were also characterized using various methods.     

Synthesis of bismuth titanate by citrate method

A simple citrate gel route was adopted for the preparation of bismuth titanate (Bi₄Ti₃O₁₂) powders. Stoichiometric quantities of BiCl₃ and TiOCl₂ were mixed with required amount of citric acid, and the mixture was heated on a water bath. This leads to formation of gel, which was decomposed at 673 K. Formation of bismuth titanate was observed on calcining powders at 973 K by X-ray diffraction studies. The average particle size is found to be 20 nm by microscopy. The room temperature dielectric constant is found to be 175 at 1 kHz. The hysteresis loop parameters were also obtained by home built Sawer-Tower circuit.     

Synthesis and sintering of barium titanate fine powders by ultrasonic spray pyrolysis

Crystalline, spherical barium titanate fine powders with a narrow particle size distribution were prepared by ultrasonic spray pyrolysis. The stability of the starting solution was influenced by type of barium source and peptizer. The particle structure was influenced by the pyrolysis temperature of the barium source. The particle structure derived from barium acetate was dense, while powders derived from barium nitrate involved a lot of hollow particles. As-prepared powders were crystallized to a perovskite structure. Inductively coupled plasma analysis showed that the BaO/TiO₂ molar ratio of as-prepared powders was 50.5:49.5. The effects of the concentration of the starting fluid, pyrolysis temperature and flow rate of carrier air through the furnace on powder characteristics such as particle size, size distribution and crystal phase were investigated. The particle size depended on the concentration of starting solution and the flow rate of carrier air, but the particle size distribution was independent of these variables. Single-phase BaTiO₃ was obtained at more than 700°C. The relative density of barium titanate sintered at 1200°C was 98%. The hollow particles in the powders resulted in a low sintering density and a large grain size. The dielectric constant and tan δ of barium titanate at 25°C were 4500 and 0.02, respectively.     

A modified method for barium titanate nanoparticles synthesis

In this research, a modified, cost effective sol-gel procedure applied to synthesize BaTiO₃ nanoparticles. XRD and electron microscopy (SEM and TEM) applied for microstructural characterization of powders. The obtained results showed that the type of precursors, their ratio and the hydrolysis conditions had a great effect on time, temperature and therefore the costs of the synthesis process. By selection, utilization of optimized precursor's type, hydrolysis conditions, fine cubic BaTiO₃ nanoparticles were synthesized at low temperature and in short time span (1 h calcination at 800 °C). The proposed procedure seems to be more preferable for mass production.The result indicated that the polymorphic transformation to tetragonal (ferroelectric characteristic) occurred at 900 °C, which might be an indication of being nanosized.     

Preparation of barium titanate nanocube particles by solvothermal method and their characterization

Barium titanate (BaTiO₃) nanocube particles below 20 nm were prepared by solvothermal method. A selection of organic solvent and inorganic materials of Ba and Ti sources was most important for the preparation of nanocubes. A nucleation and particle growth of BaTiO₃ nanoparticles led to a formation of the BaTiO₃ nanocubes with a size of 10–15 nm at temperatures above 200 °C.     

Preparation of barium titanate by homogeneous precipitation

The barium titanyl oxalate, which was the precursor of barium titanate, was prepared by homogeneous precipitation using the diethyl oxalate as a precipitating agent. The oxalate dried at 80 °C was the crystalline phase, which was converted to amorphous-like phase after drying at 120 °C. The weight loss of oxalate was 47.3 wt%. The chemical formula of the oxalate could correspond to BaTiO(C₂O₄)₂ · 4H₂O. The barium titanate obtained from the calcination of oxalate at 850 °C was a tetragonal phase with a particle size of 0.2 m.     

Synthesis and properties of barium titanate stannate thin films by chemical solution deposition

Barium titanate stannate (BaTi_1−x Sn _x O₃, 0 ≤ x ≤ 0.25) thin films were deposited directly on copper foil substrates via a chelate chemical solution process. The films were subsequently crystallized in a reducing atmosphere such that substrate oxidation was avoided and that the 2-valent state of tin could be stabilized. Despite the stabilization of the low-melting temperature SnO oxidation state at high temperatures, the final grain size was smaller with increased tin incorporation similar to other B-site substituted BaTiO₃ films. Temperature and field-dependent dielectric measurements revealed a reduction in dielectric constant and dielectric tuning with increasing tin concentration. The reduction in permittivity with reduced grain size is consistent with the well-known trends for ceramic barium titanate and in combination with a defect-dipole model involving Sn acceptors, can be used to explain the experimental trends. Phase transition frequency dependence was studied and for compositions containing up to 25 mole percent tin. No phase transition dispersion was observed and thus no strong evidence of relaxor-like character. The phase transition became increasingly diffuse with deviation from Curie–Weiss behavior, but the observed transition temperatures agreed well with bulk reference data.     

Fabrication and characterization of fine-grained barium strontium titanate ceramics by the heterogeneous precipitation method

The heterogeneous precipitation method has been successfully used to prepare SrCO₃ nanoparticle-coated BTO (BaCO₃ or TiO₂) powders by using PAA (polyacrylic acid) and NH₄HCO₃ as the dispersant and precipitator, respectively. Compared to the mixture obtained by the direct ball milling of the BaCO₃, SrCO₃ and TiO₂ powders during the conventional solid-state process, this coated structure is effective for the low temperature synthesis of barium strontium titanate (BST) powders. Sintering study of the powder synthesized by this method showed the dense and fine-grained BST ceramics could be obtained at a low sintering temperature. The grain size effect on the sensitivity of the dielectric constant vs. frequencies was discussed for the first time. Compared to the coarse-grained material, the fine-grained sample exhibits the better sensitivity of dielectric constant vs. frequency at ferroelectric state. It was shown that as the grain size decreased, the transition became diffuse, transition temperature (T _c) decreased and the dielectric constant increased.